This application claims the priority of Russian Patent Application No. 2003108508, filed on Mar. 28, 2003, in the Russian Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
Apparatuses and methods consistent with the present invention relate to multimedia and radio electronics, and more particularly, to methods and apparatuses for reconstructing the high frequency part of an audio signal to improve the quality of the audio signal.
2. Description of the Related Art
There are known methods and systems to increase the quality of audio signal, perceptible by an audience, by recovering the characteristics of the high frequency part, which were lost during transmission in channels with low carrying capacity or during encoding. The method of reconstructing missed information in an audio signal, described in Pat. No. RU 2,194,361, provides for the use of a special encoding system and digital data decoding, wherein digital data are divided on blocks of digits in decreasing order of significance of digit position, and allows reconstructing the structure of the blocks with enough accuracy.
The more simple methods are based on generation of a correcting signal by processing the remaining low-frequency part and adding the correcting signal to the original signal. For example, U.S. Pat. Nos. 6,335,973 and 6,023,513 propose to perform the generation of high-frequency harmonic from the low-frequency part of the signal. Usually, nonlinear transformations are used for this purpose. Also known is high-frequency part generation based on a high frequency noise generator, in which noise parameters are selected by an analysis of the low-frequency part of the signal (see U.S. Pat. No. 5,754,666). However, a method is described in U.S. Pat. No. 5,893,068 to perform signal transfer in the frequency domain by Fourier transformation. High-frequency addition is achieved from an expansion of the low-frequency part of a spectrum. Nevertheless, due to hearing peculiarities and namely due to the fact that the frequency resolution of the ear decreases with the sound frequency increase, simple expansion or spectrum shift will not allow for hearing perception close to the original signal.